Absolute Beginners - Summer Skies

Warm summer nights are a good time to begin learning your way around the sky. Look up as darkness falls at this time of year and you will see a brilliant blue-white star sparkling overhead. If you saw the film Contact or read the novel by Carl Sagan, this is Vega: the star that the character played by Jodie Foster supposedly travels to.

Vega forms one corner of a huge triangle of stars popularly known as the Summer Triangle, which dominates the summer sky. It's completed by Deneb and, closest to the southern horizon, Altair. If you move your mouse over this picture of the Summer Triangle, you can see the stars labeled.

I said that Vega is blue-white. If you can't immediately notice any color, try comparing it with another bright star, Arcturus, lower in the west, which has a warmer orange tone. A lot of people think of all stars as white, so it might be surprising to see these colors. A star's color is a guide to its temperature - the hottest ones are the bluest and the coolest ones are the reddest.

Star colors are more noticeable through binoculars, since they make the stars appear brighter. If you're still having trouble seeing the color, try putting the star images slightly out of focus, so that they become small disks rather than simply points of light.

Vega is the brightest star in Lyra which represents the lyre or harp played by the legendary musician Orpheus. Next to Lyra lies a large cross-shaped constellation, with Deneb at its head. It's sometimes called the Northern Cross. However ancient astronomers thought of this figure as a swan flying through the summer sky. Deneb is the swan's tail and the long bar of the cross is its neck, stretching towards the southwestern horizon. According to Greek myth, Cygnus represented the god Zeus in disguise on his way to a love tryst. Click to see a diagram of Cygnus and Lyra.

The third star of the Summer Triangle, Altair, is in the constellation Aquila, representing the eagle that carried the thunderbolts of Zeus.

The faintly glowing band of the Milky Way runs through Cygnus. The stars in the Milky Way are actually distant members of the galaxy in which we live. On clear nights you can make out a division in this part of the Milky Way, caused by a dark lane of dust between us and the stars behind it.

The long neck of the swan points towards the bright star Antares low in the south. Antares is a reddish-colored star, marking the heart of Scorpius, the scorpion. It's easy to imagine the shape of a scorpion with a curving tail among the stars here, but you'll need to be south of latitude 40 degrees to see it in its entirety.

Between Vega and Arcturus lies Hercules, the strong man of mythology, although his stars are not particularly bright. Follow an imaginary line in the opposite direction, from Vega through Deneb, and you will come to the Square of Pegasus, a well-known feature that is better-placed later in the year.

Incidentally, the term "Summer Triangle" applied to Vega, Deneb and Altair is somewhat misleading, as they remain visible well into the fall.